lover vs fancy woman

lover and fancy woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
lover	Yes	No	No	No
fancy woman	Yes	No	No	No

As nouns, fancy woman is a hyponym of lover; that is, fancy woman is a word with a more specific, narrower meaning than lover:

lover: a significant other to whom you are not related by marriage
fancy woman: an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man

Other hyponyms of lover include fancy man, paramour, man, kept woman, mistress.

lover (noun)	fancy woman (noun)
a person who loves someone or is loved by someone	an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man
an ardent follower and admirer	a woman who engages in sexual intercourse for money
a significant other to whom you are not related by marriage